The human visual system is sensitive to a specific range of electromagnetic radiation, which we perceive as light. This range, commonly known as the visual frequency band or the visible spectrum, is relatively narrow compared to the full electromagnetic spectrum.
The visible spectrum spans wavelengths from approximately 400 to 700 nanometers (nm). This range corresponds to different colors that we can perceive, from violet at the shorter end to red at the longer end of the spectrum. Beyond these wavelengths, the electromagnetic radiation is either of higher energy (such as ultraviolet) or lower energy (such as infrared), and our eyes are not sensitive to these wavelengths.
The reason for our narrow visual frequency band is primarily due to the evolutionary adaptation of our visual system. Our eyes have evolved to detect and process the specific range of wavelengths that are most informative for our survival and interaction with the environment.
One important factor is the composition of our atmosphere. The Earth's atmosphere is relatively transparent to the wavelengths within the visible spectrum, allowing light in this range to reach the surface effectively. This transparency is influenced by various atmospheric gases, such as oxygen and nitrogen, which absorb and scatter light differently at different wavelengths.
Additionally, the sensitivity of our visual receptors, known as cone cells, is optimized to detect the wavelengths that provide the most useful information about our surroundings. We have three types of cones that are sensitive to different portions of the visible spectrum, allowing us to perceive a range of colors. This trichromatic vision is well-suited for our needs, as it enables us to discriminate various objects, identify ripe fruits, detect subtle changes in the environment, and recognize facial expressions, among other visual tasks important for survival.
It's worth noting that some other animal species have different visual systems, allowing them to perceive a broader or narrower range of the electromagnetic spectrum. For example, birds and insects can see ultraviolet light, which is invisible to us. Different species have adapted to their specific ecological niches, and their visual systems have evolved accordingly.